1. Field of the Invention
The present invention relates to a refrigerating machine oil composition, more particularly to a refrigerating machine oil composition having good miscibility (or compatibility) with a hydrogen-containing Flon compound (fluoroalkane) such as 1,1,1,2-tetrafluoroethane (hereinafter referred to as "Flon 134a") capable of replacing conventional Flon compounds such as dichlorodifluoromethane (hereinafter referred as "Flon 12") which have been blamed for environmental pollution, and also having an excellent wear resistance, lubrication performance and stability in a Flon atmosphere.
2. Description of the Related Arts
In recent years, there have been reported that polyoxyalkylene glycol derivatives are highly miscible with hydrogen-containing Flon refrigerants such as Flon 134a which do not cause environmental pollution and will be useful as a lubricating oil in refrigerators using these hydrogen-containing Flon refrigerants (Specification of U.S. Pat. No. 4,755,316).
However, the polyoxyalkylene glycol derivatives have also been found to be a serious problem when used in connection with refrigerating machine such as automobile air conditioners and refrigerators because the compounds have a low wear resistance and are responsible for increases in the wear loss of friction surfaces between aluminum part and steel part (aluminum-steel friction surfaces) of the refrigerating machine in an atmosphere of said refrigerants. These friction surfaces are an important element in lubrication, consisting of the contact surface between the piston and the piston shoe or between swash plate and the shoe portion in the case of a reciprocating compressor, or consisting of the contact surface between the vane and the housing portion in the case of a rotary compressor.
Various different improvers of wear resistance have been well-known, but there has been no known means to prevent the wear loss of the aluminum-steel friction surfaces without adversely affecting the stability of the surfaces under the special condition of a Flon atmosphere.
The present inventors have made intensive researches and investigations with a view to developing a refrigerating machine oil (a lubricating oil) which has high miscibility with hydrogen-containing Flon refrigerant such as Flon 134a, is excellent in the lubrication performance and is effective for the improvement of the wear resistance, especially the wear resistance of the aluminum-steel friction surfaces. As the result, it has been found that the above-mentioned objects can be achieved by mixing a specific carboxylic acid metal salt with a specific base oil. The present invention has been completed on the basis of this finding.